1. Field of the Invention
The present invention generally relates to bypass plungers for lifting fluids from an oil or gas well that has insufficient pressure to sustain production, and more particularly to an improved latch for a two-piece ball and sleeve bypass plunger.
2. Background of the Invention and Description of the Prior Art
Two piece ball and sleeve bypass plungers are simple devices well-known in the art. The hollow sleeve includes a spherical seat in its lower end formed to match the spherical surface of the ball, thereby forming a ball check valve when the ball is seated against the seat in the sleeve. In use, the ball portion is dropped into a well first, followed by the sleeve portion. Both portions free fall toward the bottom of the well. When the sleeve contacts the ball at the well bottom, the ball is retained in the sleeve portion by a latching mechanism disposed in the sleeve, thereby holding the ball check valve closed. When the pressure of the gas in the formation is sufficient to lift the plunger, the plunger ascends toward the surface. There, a lubricator structure dislodges the ball portion from its latch and releases it to fall downward into the well, followed soon thereafter by the sleeve.
Ball and sleeve plungers are typically equipped with a latch that retains the ball against its seat during ascent of the plunger in the well tubing. The ascent is often not smooth, but subject to substantial jarring impacts that may cause the ball to become unseated if it is not latched in position against its seat. Further, in situations where the plunger is exposed to pressure differentials that may be sufficient to dislodge the ball from its seat, a latch resists such forces so that the plunger may continue to operate properly as it ascends. It should be apparent that a latch of some kind is an essential feature of a ball and sleeve plunger.
As a point of reference in this discussion and the description that follows, it is understood that the axis of a retaining ring passes through the center of the ring and is normal to the diameter of the ring. Thus, an “axial” dimension is parallel to the axis of the retaining ring and a “radial” dimension is oriented along a diameter of the retaining ring.
In a conventional design the latching mechanism in a ball and sleeve plunger typically includes a pair of standard retaining rings—aka “snap rings”—disposed side-by side in a single deep groove cut into the inside wall of the seat of the sleeve portion of the plunger. The standard rings are formed as thin rings wherein the body of the ring has a rectangular cross section whose long dimension (in the radial direction) is greater than its short dimension (thickness of the ring) that is parallel to the axis of the ring. This form requires that the groove depth extend substantially through the wall thickness of the sleeve, reducing the wall thickness by approximately 50%. This arrangement weakens the wall of the sleeve, making the sleeve susceptible to premature failure—i.e., well before the sleeve itself is worn out from many cycles of use—when it encounters the high impact force as it contacts the bumper at the end of its descent.
What is needed is a latching system that does not weaken the wall of the sleeve portion of a ball and sleeve bypass plunger to extend the useful life of the plunger.